The surface of kevlar fiber was modified by phosphoric acid solutions (H3PO4) in this article. The structure and morphology of the modified fiber were characterized by Fourier transform infrared spectroscopy (FTIR) and scanning electron microscope (SEM). The results showed that some polar groups were introduced into the molecular structure of aramid fibers. The interfacial properties of aramid fiber/epoxy composites were investigated by the single fiber pull-out test (SFP). The results showed that the interfacial shear strength (IFSS) of aramid/epoxy composites was remarkbly improved after surface modification and the breaking strength has not been affected appreciably. It provided an efficient method to make the surface modified Kevlar fiber for the application for the advanced composites at a lower production cost.